Alkylation improvement through alkylate recycle



June 2, 1970 E. T. TREGILGAS 3515770 ALKYLATION IMPROVEMENT THROUGH ALKYLATE RECYCLE Filed April 23, 1968 United States Patent Office Patented June 2, 1970 3,515,770 ALKYLATION IMPROVEMENT THROUGH ALKYLATE RECYCLE Edward T. Tregilgas, Palos Verdes Estates, Calif., as-

signor to Atlantic Richfield Company, Philadelphia,

Pa., a corporation of Pennsylvania Filed Apr. 23, 1968, Ser. No. 723,417 Int. Cl. C07c 3/54 U.S. Cl. 260-683A8 1 Claim ABSTRACT OF THE DISCLOSURE An improvement for conventional alkylation processes in which a low molecular weight olefin and a low molecular weight parain are mixed and contacted with an acid catalyst at controlled temperatures, wherein a portion of the alkylate hydrocarbon efuent is mixed with the feed prior to contact with the acid catalyst for improving the performance number of the alkylate product.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to petroleum refining processes in general. More particularly, this invention relates to acid catalyzed alkylation processes.

Description of the prior art Acid catalyzed alkylation processes are well known in the art and are conventionally used as one of several steps for producing high octane fuels. Alkylation processes are particularly important in the production of aircraft fuels. The process basic to this invention is conventionally carried out by the alkylation of low molecular Weight isoparaflins by olens to form higher isoparafns. The reaction proceeds readily with high yields at room temperature in the presence of Friedel-Craft type compounds and strong acids such as chromium chloride, zirconium tetrachloride, boron triuoride, sulfuric acid and hydrouoric acid. Of the commercial processes, the sulfuric acid and hydrouoric acid contact processes are by far the most important. The reaction product obtained with either catalyst does not consist entirely of the hydrocarbon expected by the direct addition of the olen and the isoparain. As a result of a rather complex and still not definitely established mechanism, a mixture of wide boiling point spread is obtained. By a proper choice of operating conditions, however, the product can be made to fall mainly within the gasoline range.

The basic process which underlies the present invention has been described in numerous articles, patents, and texts. Reference is made to Chemical Technology of Petroleum by Gruse and Stevens, McGraw-Hill, New York, 1960; Conversion of Petroleum, Sachanen, Reinhold, New York, 1948; and the publications and the patents cited therein for complete discussions of the theoretical and practical operation of alkylation processes of the type under consideration.

It is conventional commercial practice, as described in the cited publications and others, to use two or more alkylation units simultaneously. Each alkylation unit may conventionally include two or more acid contactors. Conventionally the output of each acid contactor and the output of each alkylation unit is combined with the other outputs and fractionated prior to blending for use ultimately as a high performance engine fuel.

Continuing efforts are made to improve the performance rating of such engine fuels. The performance rating is related to the octane but more accurately indicates the dynamic performance characteristics of such fuels. Performance ratings may be, for example, typically 100/ 130 or /145, the latter being designed for higher performance engines. The first number, 100 or 115 respectively, represents the lean mixture performance rating and is measured under simulated cruise conditions. The higher of the two numbers, and 145 respectively, represents the rich mixture performance rating and is measured under simulated conditions of load such as would occur during takeoff, climb, or acceleration. Conventionally, the precise performance rating of the ultimate fuel is obtained by blending fuels of higher and lower performance rating to produce the desired uniformity in fuel quality. The cost of such fuels is dependent in large measure upon the amount of higher performance rating fuel which must be blended into the mixture to provide the desired standard performance rating. It is a principal object of this invention to provide a method for improving the performance rating of high performance number alkylate fuel components.

SUMMARY OF THE INVENTION It has been discovered that an unexpected increase in performance rating results when a portion of the alkylate output of the alkylation unit is recycled and mixed with the feed to the alkylation unit prior to contacting the feed with the catalytic acid. Accordingly, it is the object of this invention to provide an improved process for increasing the performance number of alkylate fuels by introducing into the feed of an alkylation unit raw alkylate from the same or a different alkylation unit.

Other objects of the invention will be apparent from the specification and from the drawing to which reference is now made.

BRIEF DESCRIPTION OF THE DRAWING The single gure illustrates an exemplary embodiment of the present process showing in schematic form the flow system wherein said process is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENT A typical system in which the present process may be utilized is illustrated in the figure; however, it is to be understood that this is merely exemplary of a particular system wherein the process may be applied and is not limiting since the process of this invention is applicable to alkylation processes in general.

In a specific embodiment, the feed, a mixture of low molecular weight isoparains and olefins, is introduced through line 10 and ows through heat exchanger 12 and through line 14 to heat exchanger 16 and then through line 18 to a Chiller 20. The chiller 20 is connected to a source of compressed ammonia through line 22 for reducing the temperature of the feed to the desired input operating temperature and for removing the moisture from the feed stream after the stream has passed through line 24 to the dehydrator 26. The dried stream flows through line 28 and, in the particular embodiment under consideration, is split into lines 30 and 32 for being fed into acid contactors 34 and 36 where the hydrocarbons contact catalytic material, typically, sulfuric or hydrouoric acid, which is introduced through lines 38 and 40 respectively.

The operating temperature of the contactors is maintained by flowing compressed ammonia through lines 42 and 44, respectively, to the refrigeration units on the top of the contactors and withdrawing expanded gaseous ammonia through lines 46 and 48. Conventionally, the contactor operates in the temperature range of from about 45 to about 50 F. The alkylate efuent is removed through lines 50 and 52 and combined in line 54. The alkylate is then fed to the first acid settler 56 and then through line 58 to the second acid settler 60. The acid, in the present embodiment, being sulfuric acid, is recovered through lines 62 and 64 and combined in line l66. A portion of the spent acid is removed from line 66 through line 70 and the major portion of the acid is recirculated by means of pump 72 through line 74 to the input lines 38 and 40 as previously described.

The alkylate is taken out `of the system by means of line 76 from the second acid settler 60. The alkylate flows through the heat exchangers 16 and 12 sequentially for reducing the temperature of the input feed and then through line 80 to the caustic wash unit as in a conventional system. The alkylate is then fractionated prior to blending into the ultimate fuel.

To this point, the alkylation unit is conventional and known in the prior art. It will be apparent that this prior art example of an alklation unit is merely exemplary of the type of unit with which the present invention to be described may be used. Normally, sulfuric acid or hydrofluoric acid contactors are used but it is clear that the type of alkylation catalyst involved is of no consequence insofar as the present invention is concerned.

The application of the present invention is illustrated by the following addition to the conventional system. A portion of the raw alkylate from line 76 is withdrawn through line 82 and recycled through pump 84 and fed through line 86 to the injection point 88 just prior to the contactors. The raw alkylate `may be recycled through line 90 to the injection point 92 if it is desired to further reduce the temperature of the recycled raw alkylate and to utilize the same chilling unit and dehydrator. All or only part of the recycled alkylate stream may iiow through line 90 to be introduced into the feed stream line 18 at point 92. Insofar as the present invention is concerned, the process operations are obviously equivalent and the choice of recycle injection point will depend upon the particular system to which the process modification is to be applied.

It is to be emphasized that While, in the foregoing embodiment, raw alkylate is withdrawn from the output of a single alkylation unit and recycled to the feed of the same unit, raw alkylate may be withdrawn from another unit as well. In actual operation Where several alkylation units feed into a lesser number of caustic wash units and fractionators this latter source of raw alkylate may be preferred. The source of raw alkylate has not been found to be of particular consequence insofar as the present invention is concerned.

As previously noted, the prior art teaches the premixing of low molecular Weight isoparaflins and oleiins as a feed to the alkylation unit. For example, conventional practice is to mix ethylene with propane, for the production of isopentane or n-pentane, or with n-butane to produce 3-methylpentane or n-hexane, or with isobutane to produce 2,2-dimethylbutane or Z-methylpentane. Conventionally, also, propylene is mixed with isobutane to produce 2,2-dimethylpentane, Z-methylhexane and 2,2,3-trimethylbutane. Of course, these are merely the major components of the alkylate product stream.

lt has not been the practice, however, to recycle the product of the alkylation process into the feed and, indeed, no theoretical consideration would suggest this step.

Unexpectedly, however, when a portion of the raw alkylate product stream is recycled there is a measurable increase in performance rating of the output fuel.

Typically, the input feed to the alkylation unit consists of approximately parts of olen and 240 parts of the isoparain, preferably isobutane. In the preferred embodiment, from to 60 parts of alkylate recycle is mixed 'with the feed stock. Complete data as to the optimum ratio of alkylate recycle stock to olefin-isoparafn stock are not available but it is believed that maximum product im- 4 provement results when about 40 parts of alkylate recycle are intermixed with about 340 parts of the olefinisoparaffin feed, of the previously stated composition. These values are exemplary of the embodiment and serve to illustrate a specific embodiment of the process. It will be understood however, that since at present detailed data on a large number of feed stocks and alkylate recycle ratios are not available, the foregoing data are notlimiting as to process conditions.

The unexpected improvement in performance number rating is illustrated in the table.

TABLE 6 Performance Number 2 Improved Example l Reference 3 process Improvement 1Data obtained by recycling collected alkylate ata ratio of 20 parts of alkylate to 340 parts of conventional feed.

2 Lean mixture rating/rich mixture rating.

3 Performance number of alkylate immediately prior to addition. Similar data taken immediately after the addition were comparable.

To date, no explanation is available for the ,unex-M pected increase in performance rating but it is believed j experimental data are available, the significant and unexpected increase in performance rating resulted. It willbe apparent that, in light of the foregoing specification necessary modiications in commercial and experimental alkylation processes may be made to take advantage of the concept of the invention and that the invention is not limited to the exemplary process embodiment described hereinbefore. Accordingly, departures from the exemplary embodiment may be made without departing from the spirit and scope of the invention as defined in the following claim.

I claim:

1. In a sulfuric acid or hydrouoric acid catalyst alkylation process wherein an oleiin-isoparaflln feed is introduced into an alkylation zone and an alkylate effluent stream is removed therefrom and separated into a raw` alkylate hydrocarbon phase and an acid phase, the im-v provement wherein 20 to 60 parts by volume of said hydrocarbon is being recycled and mixed with 340 parts byvolume of oleiin-isoparaflin feed stock and said hydro` carbon and feed stock mixture is passed through the al kylation zone whereby the performance number of the` alkylate product is thereby improved.

References Cited DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner U.S. Cl. XJR.

Holzman et al. 26a-683.48 

